Behavioral flexibility is critical for adaptation to changing environments faced in every-day life;it allows animals to change behavioral strategies to suit the different demands or contingencies present at the time. Extinction learning is critical for behavioral flexibility, which is defined as the suppression of a previously expressed behavior following a change in response contingency (removal of reinforcement/punishment). Behavioral flexibility has been found to be impaired in individuals with psychiatric disorders including PTSD and also in marijuana users. These alterations in flexibility and extinction can be detrimental to normal intellectual and social functioning, and may be implicated in behavioral patterns of continued drug use. Marijuana (Cannabis sativa) is the most widely used illicit substance in the U.S.: over 14 million Americans 12 years or older report past 30-day use and 11% of 8th graders and 32% of 12th graders report past year use. Marijuana use is associated with several adverse effects, including deficits in learning and memory that are attributable to the action of delta-9-tetrahydracannabinol (?9-THC). ?9-THC is one of a group of exogenous cannabinoids that binds to and activates CB1 cannabinoid receptors that are widely distributed throughout the CNS. The body produces endogenous cannabinoids (endocannabinoids) that also activate these receptors. The primary endocannabinoids are anandamide and 2-arachydonylglycerol (2-AG) and they are rapidly broken down by the respective catabolic enzymes, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). Exogenous and endogenous cannabinoids exert their effects on learning and memory through CB1 receptors in brain regions, such as the amygdala, hippocampus, and prefrontal cortex. The goal of this project is to investigate alteration of extinction learning through the endocannabinoid system in specific brain regions using a mouse spatial learning extinction model. Mice will be trained to navigate to a hidden escape location in a maze model, and then assessed in extinction. Approaches will use pharmacological tools to target catabolic enzymes responsible for the degradation of 2-AG, along with specific receptor antagonists to examine the receptor mechanism of action. This approach is highly novel, as almost no in vivo learning studies have targeted MAGL to elevate 2-AG. Stereotaxic surgery will be utilized to administer drugs to specific brain areas of interest including the amygdala. LC-MS quantification of 2-AG collected via in vivo microdialysis will be used to examine endocannabinoid elevation in response to pharmacological agents. These studies will help to further elucidate the role of 2-AG in specific brain regions related to behavioral flexibility and specifically extinction learning. PUBLIC HEALTH RELEVANCE: Impairments in behavioral flexibility are a hallmark symptom of both individuals with post-traumatic stress disorder (PTSD) and individuals who use marijuana. These impairments cause problems in social and intellectual functioning also may contribute to patterns of continued drug use over time and marijuana continues to be one of the most widely abused drugs in the US, with over 14 million Americans reporting past 30 day use. The endocannabinoid system's role in this type of learning needs to be examined to further understand these deficits, and how to treat them.